This invention pertains to waste water pump stations, such as are used in municipal sewage systems, and in particular to a method for automatically causing a circulation of waste water within the station, coincident with pump start-up and, subsequently, automatically halting the circulation, as well as to a novel valving device for use with the method.
As is described in the Swedish Patent Application 7908743-3, sludge banks occur in waste water pump stations, and other such tanks, in sewage systems, because the waste water circulation is poor. Sludge banks cause troublesome problems, such as bad odors, a risk of explosion, corrosion, and the like. According to the cited patent application, the noted problems are solved by arranging a valve in communication with the pump outlet, the valve opening temporarily to cause waste water circulation within the station, and flushing thereof. By this means, the sludge banks are dissolved and the fluid in the station is well homogenized.
The aforesaid valve is controlled, electrically, with a linear motor which displaces a slide in the valve. There is a disadvantage to this arrangement, in addition to the relatively high cost thereof. The slide can easily become clogged, as the pumped medium in the station normally contains considerable solid bodies such as stones, rags, and similar objects. If the valve slide becomes stuck, by a stone or other, it fails to function, and the motor can break down. Too, in that the motor is electrically powered, there are installations where it is unacceptable as explosive gases are present.
In Swedish Patent No. 8900597-9 there is disclosed an arrangement in which only pump pressure is used to control the valve. Therein, pressure created by the waste water flow moves a flapper element into a closed position after a given period of time. This arrangement has the disadvantage, however, that all too often the fluid pressure is too weak to be able to move the element to a closed position.
It is an object of this invention to set forth a method for automatically circulating, and then halting circulation of waste water in a waste water pump station, and to disclose a novel valving device for use with the method, which are simple and reliable, independent of the pressure level in the station.